A conventional open wrench is shown in FIG. 7 and generally includes a body 40 having two faces 41 and a curved face 42 which is connected between the two faces 41. When the two faces 41 clamp an object 30 and the body 40 is rotated, there are gaps between the object 30 and the two faces 41, such that the corners of the object 30 are worn out by the two faces 41 and become rounded corners.
Taiwan Utility Model No. 088220749 invented by the present inventor, which discloses an open wrench with four faces for clamping a hexagonal object. Two of the four faces are parallel to each other, and an angle of degrees is defined between the other two faces. Each of the two parallel faces has at least one tooth and at least curved face, and three curved faces are formed at the connection portions between the four faces so that the object can be securely clamped and driven. When the open wrench is rotated to drive the object, the corners of the object are protected from being worn out by being positioned in the two curved faces and the three curved faces. There are two parallel sides, two faces, teeth two curved recesses and three curved recesses. In other words, there are five factors (two parallel sides, two faces, teeth two curved recesses and three curved recesses) to form the open wrench. There are over forty different specifications for the objects, including the objects of Metric and English systems. If each open wrench needs to set the five factors, the manufacturers have to spend significant time and cost to manufacture the open wrenches for all of the objects of different sizes and systems.
The present invention intends to provide an open wrench which needs only four factors to be set so as to reduce the time and cost required.